As illustrated by FIGS. 1A, 1B and 1C, a common prior art LED mounting arrangement results in a substantial portion of the light output going upwardly in the direction of a normal to the top surface of a semiconductor photonic chip 12 as seen in FIG. 1B. As seen in FIG. 1A, a top view of an LED 10, the semiconductor photonic chip 12 is mounted on a substrate 14 which is in turn mounted on a bonding pad 16. The chip 12 is encapsulated beneath an optical lens 18 which focuses the light emitted by the chip 12.
FIG. 1B shows a side view of LED 10 with a plurality of light rays relative to a normal, N, to the top surface of chip 12 illustrating the light emitted by chip 12 as it passes out of lens 18. LED 10 is an XLamp™ 7090 from Cree, Incorporated.
FIG. 1C shows an illustrative plot of the light emitted by LED 10 with the y-axis representing the intensity, I, and the x-axis representing the angle, θ, of the emitted light with respect to the normal, N, of FIG. 1B. As illustrated in FIG. 1C, a substantial portion of the light emitted from the LED is along or near the normal, N. Conversely, only a small percentage is emitted sideways. Angle α, the angle of intensity, is equal to 2*θ.
For further details of exemplary prior art LED packages with the bulk of the light intensity emitted near the normal, N, see, for example, the product literature for the XLamp™ 7090 from Cree, Incorporated.
In regard to FIG. 1B, the angle of intensity revolves around the normal, N, forming a cone of light. A photonic chip may be specifically manufactured to primarily emit white light. Some of these photonic chips may emit a disproportionate amount of yellow light near the edges of the cone of light whereas light emitted at other angles within the angle of intensity emit primarily white light. When this emitted light strikes a diffuser, such as back lighting a curtain or a shield covering an LED light package, for example, yellow rings around a concentration of white light may be visible to the human eye, causing a degradation of color uniformity.
Additionally, when LED 10 is powered on, heat from LED 10 collects along the bottom surface 15 of bonding pad 16. In general, heat radiates from the bottom of photonic chip 12. For example, an LED such as LED 10 may be driven by approximately 350 mAmps and expend 1 Watt of power where approximately 90% of the expended power is in the form of heat. Conventional approaches for dissipating heat generated from an LED include active and passive techniques. A conventional active technique includes employing a fan to blow cooler air onto the back surface of LED 10. Several disadvantages of this conventional technique include its cost, its unaesthetic appearance, and the production of fan noise. One conventional passive technique includes an aluminum panel with large aluminum extrusions emanating from an outer edge of a light fixture. At least a few of the failings of this approach include added cost for materials composing the extrusions, added weight, and limited heat dissipation due to a build up of air pressure resulting from the heated air being trapped by the extrusions.